The present invention relates to a separate lubricating device for an internal combustion engine and, in particular, to a separate lubricating device which is designed to deliver a lubricating oil by means of an electronic control to an internal combustion engine, such as a relatively small two-stroke internal combustion engine that is suited for use in a portable working machine, for example, a chain saw, a bush cutter, or the like.
As the oil supply system for a two-stroke internal combustion engine (hereinafter, referred to simply as an internal combustion engine), there have been previously known two different systems, i.e.: a mixture method lubrication system wherein a lubricating oil is mixed in advance with fuel before it is fed to the intake of the engine; and a separate lubricating system wherein a lubricating oil is supplied mechanically by making exclusive use of a lubricating oil pump (see, for example, Japanese Patent Unexamined Publication H1-113510; and Japanese Utility Model Unexamined Publication H2-13111).
However, since the aforementioned mixture method lubrication system is designed to feed a lubricating oil at a predetermined mixing ratio (usually adjusted to conform with the quantity required for a high revolution speed of engine to be employed), it is difficult to adjust the quantity of lubricating oil to an optimum degree in conformity with the operating condition of engine, thus raising the problems of generating smoke or offensive odor, particularly when the engine is running at a low speed or is idling.
On the other hand, with the conventional separate lubricating system, the lubricating oil pump is driven by a motive power derived from a crankshaft of an internal combustion engine, thereby to enable an optimum quantity of lubricating oil to be fed from the discharge port of the lubricating oil pump to the internal combustion engine in conformity with the revolution speed of the engine. However, there is a problem in that a fine control in supplying a lubricating oil cannot be achieved by only controlling the revolution speed of the pump.
Furthermore, with the system for mechanically supplying a lubricating oil, since the lubricating oil pump is driven by making use of a driving force of engine, the pumping efficiency of the lubricating oil pump is caused to decrease as the revolution speed of the engine becomes higher, thus raising a problem in that it becomes impossible to supply a sufficient quantity of lubricating oil which is necessary for a high revolution speed of engine.
With a view to overcoming the aforementioned problems, the owner of the present invention has already proposed a separate lubricating device for a two-stroke internal combustion engine, which is capable of controlling the supplying quantity or supplying time of a lubricating oil based on the operating condition of engine, thereby always enabling an optimum quantity of lubricating oil to be fed to the engine with fine controlling (see Japanese Patent Unexamined Publication H10-131726).
The separate lubricating device for an internal combustion engine that has been proposed previously by the owner of the present invention is provided at a passage of an air intake system with an injector having a heating element for heating the lubricating oil, thereby enabling the lubricating oil to be injected from the injector into the passage of the air intake system, and with a lubricating control device for controlling the injection timing and the quantity of the lubricating oil to be injected from the injector into the engine.
The separate lubricating device for an internal combustion engine thus proposed has been found, however, to be less than optimal in that the self-suctioning thereof, the number of pipes required, and the heat and vibration of the internal combustion engine are not fully taken into consideration. Namely, since the previously proposed separate lubricating device has an injector for delivering and injecting a lubricating oil in response to an electric load that is disposed at a passage of the air intake system, there is a possibility that the heat of the internal combustion engine may be transmitted to the injector. If the injector is subjected to an influence of heat from the internal combustion engine, the quantity of lubricating oil to be delivered and injected from the injector may be varied, even if the same magnitude of electric load is transmitted to the injector, thus introducing an error into the control of the supply of lubricating oil.
Also, when the vibration of the internal combustion engine is transmitted to the injector, the injector may be caused to vibrate, thereby adversely influencing the delivering and injecting of lubricating oil, thus diminishing the accuracy of the control of the supply of lubricating oil, and at the same time, the durability of the injector may be adversely affected.